To begin your first novel with an appearance from Hitler disguised as an old woman is a daring gambit. In the summer of 1986, caught up in protests against the Berlin Wall, young Mexican tourist Tatiana is squeezed into a packed U-Bahn carriage when she finds herself staring into "the jowly face, the sweeping forehead, the deep-set, furnacey eyes". Elderly men in bulky coats "cut from a cloth so thick it barely dented" form a discreet guard of honour, closing in around the old woman when she disembarks and slips away - leaving Tatiana convinced that she has come face to face with Hitler, and the reader guessing. Do we believe her? What sort of novel is this going to be?

The rest of the book, in which Tatiana returns to Berlin to pursue a solitary existence in stark contrast to the bustle of her large family and the Jewish deli they run back home in Mexico, is an original and nuanced answer to the provocative questions raised by her uncanny experience. It is also a response to the fall of the wall and an outsider's portrait of Berlin's many layers of history. Like WG Sebald reborn as a young woman, she walks the city streets: crossing Alexanderplatz, a hive of regeneration bristling with cranes; picking through the flea markets flooded with East German kitsch; enjoying the meditative "thought-ironing excursion" of the S-Bahn that swoops through the city, offering "old and new, logic and impulse, grit and glamour, all blurred into one long thread". Sometimes she feels alienated from the city, sometimes cautiously assimilated, but always the weight of history presses in- as when she tours the infamous subterranean "Gestapo bowling alley", part psychic horror, part tourist trap ("Nazi, Stasi, what's the difference," shrugs the guide), or loses her bearings among the concrete slabs of the Holocaust memorial; or investigates ghostly noises coming from the empty apartment upstairs.

The novel's other characters are as solitary and disconnected as Tatiana. Dr Weiss, a historian obsessed with the coexistence of different times in the same space, whose decades-old thoughts she transcribes from Dictaphone tapes, is literally a voice from the past, as well as a frail, enigmatic presence shuffling through his darkened flat. Jonas, who would fall in love with Tatiana if she would let him, is a freelance meteorologist, living up among the clouds on the 18th floor of a towerblock. As a child in East Berlin, the sky gave him a sense of freedom: through the lovely image of his "cloud garden", he explains the lesson of flux he drew from cloud formations and applied to life during dictatorship and political upheaval. "All structures are collapsible." In a dreamy, abstract way the sky mirrors humanity's constant activity at ground level.

Indeed, weather is a key element of Chloe Aridjis's urban vision: Tatiana's narrative of Berlin opens with a storm that shakes the dust of the past up from between her floorboards and closes with a freak fog that envelops the whole city. Snow, rain, shadow and darkness also obscure her tentative portraits of people and place.

Occasionally the impressionistic scenes and untethered anecdotes can seem flat or mannered, with the automated quality of creative writing exercises, but this remains a most unusual debut. Like Tatiana, an entirely refreshing portrait of young womanhood, it is unselfconscious, uncompromising, wholly authentic: a fraying mass of narrative loose ends, it is also somehow satisfying in its open-endedness.

The mysterious chalk scores on the wall of the underground bowling alley and the sinister outline of a missing picture on the wall of the upstairs apartment are held in delicate, suggestive balance. Aridjis knows that questions linger longer than answers, and that when it comes to the past, as Tatiana discovers, "the more you try to rub something away the darker it becomes".